The invention relates to a moving-bed reactor for the treatment of fluids, in particular of flue gases from power station installations or the like, in accordance with the preamble of claim 1.
As indicated in DE 3,732,567 Al, moving-bed reactors are used for the treatment of fluids, for example flue gases, over more or less fine-grained loose materials. The loose material forms a loose-material bed moving downwards through the reactor and is fed into the reactor at the top and discharged at the bottom continuously, quasi-continuously or batchwise. In the region of the loose-material discharge from the treatment zone, a so-called inflow tray is provided which has outlet openings for the loose material on the one hand and inlet openings for the fluid to be treated on the other hand. It is essential here that the fluid to be treated is distributed as uniformly as possible in the entire moving-bed reactor, so that the moving loose material as a whole acts as an absorbtion filter, i.e. the pollutants are bound to the surface of the loose material. The technology of these absorption filter installations is adequately known and described, for example, also in WO 87/00768 with further literature references, for example German patent specification 3,228,984. The problem in moving-bed reactors of this type is, inter alia, to obtain the most uniform distribution possible of the gas to be treated within the downward-moving loose material, an optimization of the required loose-material rate being necessary. In the cited state of the art, the flow of the loose-material layer through the gas to be treated takes place in the so-called countercurrent process, i.e. the gas moving upwards flows in countercurrent through the loose material moving down in the reactor.
Furthermore, there are so-called crossflow installations, in which the loose material flowing downwards in a cylindrical or prismatic housing is penetrated transversely by the flue gas which is to be treated. In this case, the gas is fed along the entire loose-material height to the cylindrical housing by means of louvre-type slots in the housing wall. Admittedly, the crossflow installations have the advantage that in general no additional inflow trays are required in the interior of the reactor, as is the case in the abovementioned printed publications. In fact, such inflow trays serving to produce uniform distribution of the gas within the reactor have the disadvantage that the uniform downward flow of the loose material can be adversely affected. In order to ensure that all the loose material present in the reactor can participate in the reaction, it is absolutely necessary that so-called mass flux takes place throughout the reactor. For a definition of mass flux, attention is brought to the following literature reference: A. W. Jenike, Storage and Flow of Solids, Bulletin 123 of the UTAH Engineering Experiment Station University of UTAH, USA. In contrast thereto, in the case of so-called core flow, the loose material would flow off only through a flow tube surrounded by dead zones. Since, however, no solids exchange takes place in the dead zones, reaction with a gas seeping past also no longer takes place after a short time.
The known crossflow process has, however, the the disadvantage that, due to the necessary mass flux, very steep and correspondingly high outlet funnels are required, without lateral flow through the contents thereof, which therefore remain uninvolved in the reaction. A further disadvantage of the crossflow process is that two opposite cylinder walls of the reactor must be gas-permeable. At the same time, a trickling-out or blowing-out of solid must be avoided, especially on the cylinder wall located downstream. This is only insufficiently the case in the known design of the gas-permeable walls in the form of louvre-type slots or mutually overlapping plates. If screens are used in place of the plates, these also tend to block very easily. Therefore, in order to obtain an adequate gas permeability of the loose bed in the crossflow process, the use of crossflow reactors is restricted to relatively coarse loose materials having a grain size of more than 2 mm. Moreover, with continuous attrition, the not entirely avoidable dusty fines must be removed before the loose material is used again, since the dust blocks the flow channels located between the larger particles and hence causes a steady rise of the flow resistance. Crossflow reactors are therefore substantially more sensitive to attrition, which is therefore removed during regeneration and thus causes considerable costs.
The further disadvantage of the crossflow process is that the residence time of the gas is shorter than would be the case in a vessel with longitudinal flow. Both the countercurrent reactor and the crossflow reactor of the state of the art accordingly show considerable disadvantages.
If, in WO 87/00768 mentioned at the outset, a loose-material vessel is used which does not have a tapering outlet funnel in its bottom region, a mass flux is also impossible with this vessel because of the numerous internals as inflow trays, i.e. a core flow is established which leads to non-uniform flow of loose material through the vessel.
The same would apply to the cited DE 3,732,567, although this contains funnel-shaped loose-material outlets. In this loose-material outlet, however, extensive internals are inserted in the form of inflow trays, which prevent uniform flow throughout the vessel, i.e. mass flux.